A full set of traditional dumbbells has various pairs of dumbbells with different mass, e.g. a pair of 5 pound dumbbells, a pair of 10 pound dumbbells, and so on. Such dumbbells are used for weight training exercises such as biceps curls, triceps extensions, etc. Different users will use whatever size dumbbells are most suited to their particular physical condition and exercise needs. For example, one user might lift 10 pound dumbbells while another user might lift 50 pound dumbbells.
Such a dumbbell set is both costly to purchase and requires a fair amount of storage space. Storage racks are needed simply to store the various pairs of dumbbells. As a practical matter, individuals and small gyms or exercise clubs may not be able to afford either the money or the storage space required for a full set of traditional dumbbells.
Selectorized dumbbells overcome the cost and space obstacles presented by traditional dumbbells. In a selectorized dumbbell, a plurality of weights are nested together. The weights provide a stack of nested left weight plates and a stack of nested right weight plates. The left and right stacks of weight plates are separated from one another by a gap.
In a selectorized dumbbell, a handle is inserted into the gap between the left and right stacks of weight plates. A selector is then manipulated to determine how many of the left and right weight plates of the weights are coupled to the left and right ends of the handle. Once the selector is positioned to pick up a selected number of weights, the handle can then be lifted by the user from between the stacks of weight plates. The selected number of weights will rise with the handle to be used in performing various exercises with the dumbbell.
The obvious advantages of selectorized dumbbells are the cost and space savings provided to the purchaser. Only two dumbbells need be purchased and not an entire set. Yet, these two dumbbells can provide a wide range of exercise mass depending upon how many of the nested weights are coupled to the handle by the selector. Moreover, the only storage space required is that needed for two dumbbells and the nested weights that accompany them. All of this can be stored on a small rack that takes up only a few square feet of floor space. Thus, a single pair of selectorized dumbbells provides an economical alternative to a full set of traditional dumbbells.
The Applicants' own U.S. Pat. No. 5,769,762 discloses a selectorized dumbbell in which the left and right weight plates in each stack thereof are coupled together in pairs by shallow, upwardly facing channels. Each weight thus comprises one left weight plate, one right weight plate and the interconnecting channel. The channel has vertically extending front and back walls. The channels of the different weights nest inside of another when the left and right weight plates are disposed in their nested stacks. When so nested, the front walls of the channels of all the weights overlie one another along a front side of the dumbbell and the back walls of the channels of all the weights similarly overlie one another along a back side of the dumbbell.
The overlying front walls of the channels are provided with various sets of aligned holes and slots. The different sets of aligned holes and slots are unique so that different numbers of weights will be coupled to the handle and picked up when a connecting pin is inserted through one set of holes and slots. This is how one adjusts the weight of the dumbbell. The pin is inserted into that set of holes and slots that will pick up the desired number of weights.
Identical sets of holes and slots are also arranged along the overlying back walls of the channels. The pin is long enough to extend between and span the distance between the front walls and the back walls of the channels. Thus, when the pin is inserted into a particular set of holes and slots in the front walls of the channels, the pin is long enough to extend through a corresponding set of holes and slots in the back walls of the channels.
The sets of holes and slots are necessarily distributed along the lengths of the front and back walls of the channels. One set of holes and slots may be arranged along a transverse centerline of the dumbbell, i.e. a line passing through the center of the dumbbell perpendicular to the front and back walls of the channels. But, the other sets of holes and slots will inherently be set to one side or the other of this transverse centerline, i.e. will be off center relative to the transverse centerline.
When the pin is inserted into any set of holes that is off center relative to the transverse centerline, the weights are coupled to the handle in an unbalanced configuration. The weight plates that are furthest from the pin will exert a torque about the pin that is greater than the torque exerted by the weight plates that are closest to the pin. This will cause the weight plates that are furthest from the pin to slightly droop or sag relative to the handle.
This is disadvantageous as it leaves the user with the impression that the weights are not securely attached to the handle even when they are. In addition, the dumbbell can feel somewhat unbalanced to the user when the user picks it up and exercises with it. This is particularly true when the pin is inserted through one of the outermost sets of holes and slots in which the pin is the furthest away from one set of the weight plates. In this pin orientation, the sense of unbalance is at its most pronounced.
In addition, the weights are coupled to the handle using only a single connecting pin with a single connecting prong. While the prong of the pin extends all the way through the dumbbell between the front and back walls of all the channels, there is always a possibility that the pin could become accidentally dislodged during use. In this case, the weights would detach from the handle.
Accordingly, there is a need in the art for a selectorized dumbbell in which the weights would be attached to the handle by a selector that couples the weights to the handle in a balanced manner from side to side. Desirably, such a selector would have a redundant safety mechanism for helping keep the weights securely attached to the handle even if a portion of the selector were inadvertently dislodged.